【正文】 cost of mitigating it. For example, meteor damage to the data center often falls under this category. The likelihood of a meteor shower damaging the data center is so small and the cost of installing antimeteor shielding to the building is so large that most anizations choose to assume the risk rather than assuming the cost of mitigating the risk. The risk of a meteor shower destroying a data center is a possibility. Just as the risk of tornadoes, floods, and any number of unknown events are also possibilities. It is probably not cost effective to create custom solutions for every eventuality. It is much easier to create a single plan that can be implemented in any of these events. This plan is called the contingency plan. IT service continuity management starts by carefully agreeing to availability targets with the customer and determining the cost of downtime or unavailability of the IT service in question so that a realistic IT budget can be established. It is also important that the negotiation include realistic expectations of reduced system availability while the contingency plan is in place. This process involves an element of education and negotiation on both sides (the customer and the IT anization). Customers need to understand how to define and articulate their availability requirements. The IT anization needs to understand the functions that make up the overall IT service and which of them are the most critical. Identify Information Technology Service Layers To understand where risk may be introduced, the IT environment must be broken down into logical, manageable ponents. One way to do this is to divide the services provided by the IT department into layers. For the IT department, these layers are: ? Service. ? Application. ? Middleware. ? Operating system. ? Hardware. ? Local area work (LAN). ? Facilities. ? Egress. The operating system requires hardware on which to run. In turn, the operating system provides critical functions to middleware services, such as a database. Information technology cannot deliver a service (top layer) unless all of the services underneath are functioning properly. The key to providing a service is to provide the supporting IT functions required to create that service. Service This is the function that IT is helping the business perform. This likely has a name that is easy for the business to understand, such as payroll. In order to perform this function, the business needs the support of the IT layers, each of which is described in the following sections. 12 IT Service Continuity Management Application The application is the topmost layer of the IT stack. The application is the piece of IT that most users see. In order to provide a service, such as accounting, the users make use of an application, such as Microsoft Great Plains174。 people see the Web pages, but most are not aware of the services required to deliver them. Middleware Middleware can be defined as “the part of the application that the users do not see.” Middleware includes databases, Web services, and messaging systems. Given this broad definition, the question of what constitutes middleware varies greatly from application to application. In every case, however, a plete map of the middleware should be made so that targets for its availability and capacity can be accurately created. Operating System The operating system is the software that controls the allocation and usage of hardware resources such as memory, CPU, disk space, and peripheral devices. Because of this relationship between software and hardware, correct operating system performance is critical to correct application performance. The user may not be aware of the operating system or what it does, but the user is aware when critical services are not available due to poorly written device drivers and other operating system problems. Hardware Hardware, as used here, represents a wide range of ponent types. While this is not a prehensive list, it certainly contains puters and storage devices. Within each of these there can be memory, fans, power supplies, and many other device types. Regardless of how it is defined, extra hardware and spare parts need to be allocated to a data center in order to replace pieces that might fail. Local Area Network The work inside a building provides a munications backbone upon which puter systems are able to municate. For a more detailed explanation of working ponents, see the Network Administration Service Management Function guide. Examples of work ponents are discussed subsequently. Passive Components Passive ponents, such as wires and wall jacks are key to any work. These ponents must be accounted for in availability calculations, since they may occasionally break and therefore need replacing. With the increasing use of wireless working technologies, however, the use of copper cables is being less mon. Service Management Function 13 Hubs, Switches, and Routers Hubs, switches, and routers are critical to any work infrastructure. They control and route data on the work. Each must remain available and must provide sufficient capacity to meet the needs of the layers higher in the stack. Network Interface Cards Computer systems connect to the work backbone with work interface cards. These ponents are relatively inexpensive, so it is not unmon, for example, to place more than one card into each puter to provide redundancy in the event of one failing. It is also mon to direct all external Web traffic to one card and reserve the other for internal management data. Facilities Facilities consist of the building that houses the data center and any associated ponents. Examples of facilities ponents are described in the sections that follow. Edifice The physical building is obviously very important as it provides a sh